Blend close shades of colors together in compositor
I guess the following can be adjusted to your needs.

Two mesh objects, partly overlapping will be mirrored at intersections, RGB independant.



Compositing nodes create a mask of the intersections. (This part is highlighted in red.) 

Enable the Z and Object Index Pass of the render layer. (Properties Window > Scene > Passes)

Assign two different pass indices to the objects, in my case 1 and 2. (Properties Window > Object > Relations > Pass Index)

After dilating the objects masks, their overlapping part will the border between them. Multiply both masks to only retain the boundaries. If both parts are in the same mesh, you can get this mask with the Material Boundary of Freestyle (which will have correct anti-aliasing).

To exclude the parts, where the meshes overlap but are apart, check differences in the depth channel. The Prewitt or Sobel filter will give us the difference between close pixels. Where this z - difference is larger than a certain value (0.05 in my case) there is space between the objects (which we dont want to blur). Multiply the "edge" mask with Z-Difference lesser than the min value (0.05) to get the intersections.